Into a large bowl, or preferably, a food processor add the cornmeal, flours, salt, baking powder, sugar. To the dry ingredients add the butter. Using a pastry cutter or 30-35 quick pulses of the food processor, blend the mixture until it resembles tiny, sandy pebbles.

Dump the mixture into a medium bowl, add 1 1/2 cups of milk and with a fork stir just until everything is combined. You are going to roll out the dough, so if it is too wet, stir in a couple extra tablespoons of flour, if it is too dry stir in an extra tablespoon or two of milk. You don't want to overwork the dough, or your tarts will be tough, so stir only as much as you have to.

Dump the dough out onto a well-floured surface, pull it together into one large mound, and roll out until it is about 1/3-inch thick. Pat with more flour if things get sticky - sticky dough is your enemy in this recipe. Cut the biscuit dough with a medium cutter (the one I used was about 2-inches across), then cut half the rounds with a slightly smaller cutter.

Brush the large rounds with a bit of egg white - this will give the tarts that nice golden color. Place the outer rings on top, brush those with the egg white, and fill with a bit of jam.

Place the tarts on a rimmed baking sheet and bake for 10-13 minutes - larger tarts will need to bake longer. The rimmed baking sheet is important to use because these tarts tend to have a bit of runoff, and you want to prevent a mess in your oven.